Electrical bushing assembly



Jan. 14, 1969 E. E. WOODS 3,422,392

ELECTRICAL BUSHING ASSEMBLY Filed June 8, 1966 INVENTOR I Edmund E. Woods.

- @2242? fan ATTORNEY United States Patent 1 Claim ABSTRACT OF THE DISCLOSURE An electrical bushing assembly having a cast body portion, an axially extending electrical conductor, and a metallic mounting flange. The metallic mounting flange has a portion circumferentially embedded in the body portion, with a resilient member disposed between the embedded portion of the flange and the cast body portion of the bushing.

The secondary or low voltage bushings for electrical transformers of the distribution type are commonly constructed of porcelain. The conductor assembly of the porcelain type low voltage bushing, in order to accommodate a plurality of load circuits, may include a relatively large spade-type end or terminal having a plurality of openings disposed therein. The ends of the load conductors which are to be connected to the terminal are each fitted with a crimp-type connector, which is crimped to the end of the electrical load conductor, and which is adapted for connection to the spade terminal of the electrical bushing with a nut and bolt. After all of the various load conductors are fastened to the spade terminal, the terminal and connectors are insulated from ground by taping the connections with an electrical insulating tape. The taping of the connections is difficult and time consuming, however, due to their irregular configuration, and the moisture resistance of the joint depends upon the skill of the one applying the tape. Further, in order to either connect or disconnect the load conductor from the spade type low voltage terminal, the electrical transformer must be disconnected from the source of electrical potential.

It would be desirable, therefore, to provide a new and improved low voltage electrical bushing assembly and bushing cable connector which allows a plurality of electrical connections to be quickly made, with the connections being electrically insulated and sealed against moisture without resorting to insulating tape. It would also be desirable to provide a new and improved low voltage electrical bushing assembly and bushing cable connector which allows the various electrical connections to be made or disconnected after merely removing the load from the conductors, making it unnecessary to disconnect the source of electrical potential from the transformer.

Accordingly, it is an object of the invention to provide a new and improved bushing assembly for electrical apparatus.

Briefly, the present invention accomplishes the abovecited objects by providing a one-piece bushing structure formed of cast, solid electrical insulating material, which has a plurality of blind orifices or openings which extend into the bushing structure from one end thereof for receiving a plurality of plug-in type bushing cable connectors. The bushing structure has an electrical conductor embedded in the cast electrical insulating material which extends outwardly from one end thereof, with the extension being adapted for connection to the associated electrical apparatus. The electrical conductor terminates near the opposite end of the bushing, at the bottom of the blind openings in the bushing, with an electrical contact being disposed in each of the openings and secured to the electrical conductor. A metallic tubular member, having 3,422,392 Patented Jan. 14, 1969 "ice an outside diameter which is at least partially threaded, and a predetermined inside diameter, is disposed in coaxial relation with each of the openings in the bushing, with the tubular member being partially embedded in the cast solid electrical insulation material, and partially extending outwardly therefrom.

An electrical plug-in bushing connector is provided which includes an electrical cable which has the electrical insulation removed for a predetermined distance at one end thereof, and an electrical contact member disposed over the exposed end of the cable and crimped or otherwise fastened thereto. The plug-in bushing connector also includes a resilient weather tube or sleeve which is telescoped over the cable for a predetermined distance in contacting relation therewtih, and cable clamping and sealing means which is telescoped over the resilient weather sleeve. The bushing cable connector assembly is electrically connected to the bushing assembly by disposing the electrical cable and a portion of the resilient weather sleeve into an orifice of the bushing, pushing the cable into the orifice until the electrical contact fastened to the end of the cable and the contact at the bottom of the orifice are engaged, threadably connecting the cable clamping and sealing means with the metallic sleeve to compress a gasket member against the resilient weather sleeve to form a moisture seal, and clamping the cable with the clamping and sealing means to mechanically secure the cable in assembled relation with the electrical bushing. Thus, the electrical connections are completely contained within the cast portion of the electrical bushing, which electrically insulates and moisture proofs the electrical connections without requiring auxiliary taping. Also, since there are no exposed live terminals, the electrical connections may be made and broken when the electrical terminals or contacts of the bushing assembly are energized, as long as the plug-in bushing connectors are disconnected from their service or load circuits.

Further objects and advantages of the invention will become apparent from the following detailed description, taken in connection with the accompanying drawings, in which:

FIGURE 1 is an elevational view, partially in section, of an electrical bushing assembly constructed according to the teachings of the invention;

FIG. 2 is a plan view of the electrical bushing assembly shown in FIG. 1;

FIG. 3 is a fragmentary elevational view, partially in section of the bushing assembly shown in FIG. 1, including a bushing cable connector constructed according to the teachings of the invention disposed in assembled relation with the bushing assembly, and

FIG. 4 is a fragmentary elevation, in section of a bushing assembly constructed according to another embodiment of the invention.

Referring now to the drawings, and FIGS. 1 and 2, in particular, there is shown elevational and plan views, respectively, of an electrical bushing assembly 10 constructed according to the teachings of the invention. Bushing assembly 10 performs all of the functions of the conventional porcelain low voltage bushings associated with electrical distribution transformers, and may be disposed through an opening 16 in the casing 18 of electrical apparatus, such as the tank or cover of an electrical distribution transformer, and mounted or fixed in position by using conventional mounting hardware. In addition to providing the functions furnished by the porcelain-type low voltage bushing, electrical bushing assembly 10 makes electrical contact with the service or load conductors within the body portion of bushing assembly 10, instead of having exposed live terminals, which facilitates the insulating and moisture proofing of the electrical joint without resorting to electrical insulating tape.

Although bushing assembly may be advantageously utilized with any type of distribution transformer which has a plurality of load circuits connected thereto, and in any environment, its advantages make its use extremely attractive in vault mounted transformers for underground electrical distribution systems. For example, the moisture proof joints make a distribution transformer which also uses plug-in type high voltage bushings, such as those disclosed in co-pending application Ser. No. 489,339, filed Sept. 22, 1965, and assigned to the same assignee as the present application, completely submersible, and thus electrical service would not be deleteriously affected by moisture, even in the event the vault were to be flooded. Also, since all energized terminals or contacts are contained within the bushing assembly, openings in the vaults for ventilation purposes do not present a hazard to children who may poke sticks and other foreign objects into the vault. The protected electrical connections also make it possible for maintenance personnel to make and break the electrical connections without disconnecting the source of alternating potential from the transformer, as long as the load circuits are disconnected.

More specifically, bushing assembly 10 includes a cast, resinous, oil resistant body portion or member 12, which is generally elongated, terminating at first and second ends and 22, respectively, with the first end 20 extending outwardly from casing 18, and the second end 22 extending into casing 18 for connection with the associated electrical apparatus. Cast body member 12 may be formed of any suitable electrical grade resin system, preferably having filler means selected to provide a coefficient of thermal expansion which closely matches that of any metallic inserts which are to be embedded into the casting. For example, an epoxy resin system having a filler of particulated beryllium aluminum silicate, described in detail in cO-pending application Ser. No. 406,- 102, filed Oct. 23, 1964, now abandoned, and assigned to the same assignee as the present application, has been found to be excellent, possessing superior physical properties at elevated temperatures, high thermal conductivity, excellent crack resistant characteristics, and a low coetficient of thermal expansion which closely matches that of metallic inserts, such as those formed of copper, aluminum or brass. Epoxy resin systems have been found to be particularly suitable, due to their resistance to oil and other fluid coolants commonly utilized in electrical transformers, but other suitable resin systems may be used. Also depending upon the particular mechanical and electrical requirements of the intended application and environment, other suitable fillers may be used. For example, alumina trihydrate (Al O .3H O) may be used to obtain completely non-tracking characteristics.

The resin system is preferably of the thermoset type, although thermoplastic resins may be used if their softening temperature is higher than the maximum operating temperature of the bushing.

Bushing assembly 10 includes an electrical conductor assembly 14, formed of copper, aluminum, or other suitable electrical conductor. Conductor assembly 14 includes a conductive member 24 which is generally coaxially disposed with a center line 26 of body member 12. Conductive member 24 extends outwardly for a predetermined distance from end 22 of body member 12, and may include means, such as threads 28, for connecting conductor assembly 14 with the electrical apparatus disposed in casing 18. Instead of also extending outwardly from end 20 of body member 12, conductive member 24 terminates a predetermined distance from end 20, and is electrically connected to conductive member 30, which is disposed transversely to conductive member 24. Conductive member 30 may have a plurality of arms or extensions which extend outwardly from conductive member 24, with the number of arms depending upon the number of service connections which are to be made to bushing assembly 10. For example, bushing assembly 10 is cons ucted to receive four service connections, and conduc- 4 tive member 30 has four arms, 32, 34, 36 and 38. Conductive member 30 may be of one-piece construction, or it may be formed of two or more members which are suitably connected, such as by brazing or soldering.

Body member 12 has a plurality of blind openings or orifices which extend inwardly from end 20 in spaced parallel relation for a predetermined distance, such as orifices 40, 42, 44 and 46. The number of orifices is determined by the number of service connections which bushing assembly 10 will be required to make. Each of the orifices 40, 42, 44 and 46 is aligned with one of the arms 32, 34, 36 and 38 of conductive member 30, with the orifices extending to and terminating at the arms.

Each of the arm members or extensions 32, 34, 36 and 38 of conductive member 30 have a spring type tubular electrically conductive contact member or socket-like terminal 48, 50, 52 and 54, respectively, disposed thereon, which extends from a surface of arms 32, 34, 36 and 38 into orifices 40, 42, 44 and 46, respectively. Thus, each of the electrical contact members is accessible through an orifice. Each of the contact members 48, 50, 52 and 54 are substantially tubular in shape, with the centerline of the tubular contact members being coaxially disposed with respect to a centerline of its associated orifice, such as centerline 56 of orifice 40. The walls of the tubular contact members may be slotted, as shown at 58 in FIG. 2, in order to provide spring-like fingers or extensions which will firmly grip a cylindrical plug-in member which is slightly larger than the inside diameter of the tubular contact members. In order to provide good electrical conductivity, as well as the necessary resiliency, tubular contact members 48, 50, 52 and 54 may be made of beryllium copper, or any other suitable electrically conductive material. Tubular contact members 48, 50, 52 and 54 may be mechanically and electrically connected to conductive member 30 by any suitable means, such as by the rivet pin 60 shown in FIG. 1, or by brazing, soldering or other fastening means. While contact member 48 is preferably tubular, as shown in FIG. 1, and thus adapted to receive a plug-in type contact, it will be obvious that the functions may be reversed, with the contact member 48 associated with the electrical bushing assembly 10 being a plug-in type, adapted to engage a socket-like contact member.

Bushing assembly 10 also includes a plurality of tubular metallic members 62, 64, 66 and 68 which have an inside diameter extending between first and second ends, 69 and 71, respectively, which is substantially the same as the diameter of orifices 40, 42, 44 and 46. The first ends 69 of the metallic tubular members are embedded in end 20 of body member 12, with the longitudinal centerline of the tubular metallic members being disposed coaxially with the centerline of one of the orifices, such as the centerline 56 associated with orifice 40. In other words, the opening in each of the tubular metallic inserts is aligned with one of the openings in body member 12. As hereinbefore stated, only the first ends 69 of the tubular metalllc members are embedded in body member 12. Their second ends 71 extend outwardly from end 20 of body member 12, and are externally threaded as shown at in FIG. 1, for purposes which will be hereinafter explained.

Bushing assembly 10 is molded or cast to form a shoulder 72 intermediate its ends 20 and 22, which provides thefunction of aligning bushing assembly 10 relative to casing 18, and may also provide part of the mounting means for securing bushing assembly 10 to casing 18. A suitable gasket member 74 may be disposed between shoulder 72 and casing 18, to seal opening 16 against moisture. Shoulder 72 may be undercut if desired (not shown) with gasket member 74 being at least partially disposed in the undercut.

As hereinbefore mentioned, shoulder 72 may form part of the mounting means for securing bushing assembly 10 to casing 18. Shoulder 72 has a diameter larger than open- 1ng 16, and thus may cooperate with suitable fastenin means disposed on the opposite sidetot opening '16.":Th

fastening means may be the same as used for conventional porcelain type bushing, such as the metallic flexible locking ring 80 shown in FIG. 1. At least the portion of body member 12 which extends into opening 16 in the casing 18, and immediately adjacent thereto, may have a plurality of threads 82 formed thereon at the time of casting, or subsequently machined therein, which cooperate with locking ring 80 to pull shoulder 72 tightly against gasket member 74 and against the outer surface of casing 18.

Other suitable fastening means may also be used to secure bushing assembly in fixed relation relative to an opening 16 in the casing 18 of electrical apparatus. For example, bushing assembly 10 may be secured to casing 18 by electro-swaging, as disclosed in U.S. Patent No. 3,214,511, issued Oct. 26, 1965, and assigned to the same assignee as the present application. Or, in the event it is desired to weld the bushing assembly 10 to the casing 18, a metallic mounting flange may be circumferentially embedded into body portion 12 at the time of casting. FIG. 4 is a fragmentary view of bushing assembly 10 illustrating an annular metallic flange 150 which has its inner portion embedded in body portion 12. Mounting flange 150 may be formed of any metal suitable for welding. Since the welding heat may break the bond between mounting flange 150 and body portion 12, and thus allow moisture to enter casing 18 around flange 150, a high temperature 0 ring or resilient gasket member 152 should be disposed between the embedded portion of flange 150 and body portion 12. Flange 150 may have a cylindrical extension 154 to facilitate holding and locating resilient member 152 in the desired relation while the body portion 12 is being cast.

A plug-in bushing cable connector 100 for bushing assembly 10, constructed according to the teachings of the invention, is shown in FIG. 3. FIG. 3 is an enlarged, elevational, fragmentary view, partially in section, of body member 12, illustrating one of the plug-in positions of the bushing assembly, with plug-in bushing connector 100 being shown in assembled relation relative to opening 40 in body member 12.

In general, plug in bushing connector 100 includes an electrical cable 102, a resilient weather tube or sleeve 104, an electrical contact or terminal 106, and clamping and sealing means 108. Electrical cable 102 includes a central electrical conductor 110, around which is disposed a tight fitting layer 112 of electrical insulation. Electrical cable 102 may be the service cable for serving one of the load circuits to be connected to bushing assembly 10.

The electrical insulation 112 is removed from one end of cable 102 for a predetermined distance, providing a length of uninsulated electrical conductor 110. A tubular metallic contact 106 is telescoped over the end of electrical conductor 110 and fastened thereto. Contact 106 has an inside diameter which is substantially the same as the outside diameter of electrical conductor 110, and an outside diameter which cooperates with spring type tubular contact member 48 mounted at the bottom of opening 40 in bushing member 12.

Contact member 106 may be crimped to firmly engage electrical conductor 110, as shown at 114, which provides good electrical conductivity between electrical conductor 110 and contact 106, and also insures that contact 106 will be mechanically secured to electrical conductor 110. Other suitable fastening means may be used, but the means selected should be easily performable in the field where the service connections are to made to the bushing assembly.

Contact member 106 may have an annular groove 116 disposed therein, which cooperates with a radius on the extending fingers of contact member 48, which serves the function of mechanically locking contact 106 in position in the socket-like contact 48, and also provides means for indicating when plug-in connector 100 is in the desired assembled relation with bushing assembly 10. In other words, since it will not be possible to visually determine when plug-in connector is in the desired assembled relation relative to body portion 12 and contact 48, positive means must be provided which will indicate when bushing connector 100 is in the desired position. The interference fit between the fingers of contact 48 and the outer diameter of contact member 106, and the lockingin action when the contact fingers of contact 48 snap into place into annular groove 116, will provide a feel or physical sensation which will provide the desired indication.

A resilient weather sleeve 104 having an outside diameter which is substantially the same as the diameter of opening 40 in body member 12, and an inside diameter substantially the same as the outside diameter of electrical cable 102, is telescoped over cable 102. Weather tube or sleeve 104 may be formed of rubber, or any other suitable resilient material. By providing the openings in body portion 12 of bushing assembly 10 with a larger diameter than the outer diameter of any service cable that may be used with bushing assembly 10, bushing assembly 10 may be used with any smaller cable diameter by providing a plurality of weather sleeves having an outside diameter which is substantially the same as the diameter of the bushing opening, and different wall thicknesses. Thus, to connect a particular cable size with bushing assembly 10, it is only necessary to select a contact member 106 having an inside diameter which is substantially the same as the outside diameter of electrical conductor 110, and a weather sleeve 104 having an inside diameter which is substantially the same as the outside diameter of electrical cable 102.

Clamping and sealing means 108 may be in the form of a metallic clamping nut, which is formed of brass, aluminum or other suitable metal, and it has first and second inner diameters 122 and 124, respectively. Clamping means 108 is telescoped over weather sleeve 104, with the first inner diameter 122 having substantially the same dimension as the outside diameter of weather sleeve 104. The first inner diameter 122 is associated with a clamping ring which encircles the outer diameter of the clamping and sealing means 108 adjacent the first inner diameter 122, with clamping ring 120 enabling clamping means 108 to be mechanically secured to weather sleeve 104 after bushing cable connector 100 is plugged into bushing assembly 10. Clamping ring 120 may be similar to a conventional hose type clamp, having a screw member 121 and cooperating ring member 123. The inner diameter of ring member 123 may be changed by turning screw member 121 to tighten the first inner diameter 122 against the resilient weather sleeve 104. Thus, the Wall section of the clamping means 108 adjacent the clamping ring member 122 should be such that it will flex under the influence of the clamping ring member 123 to tightly grip weather sleeve 104, and may have one or more longitudinal slots to provide the desired resilient or flexing action when urged inwardly by clamping ring member 123.

The second inner diameter 124 of clamping and sealing means 108 is threaded, and has a diameter which cooperates with the outer diameter of threaded tubular member 62 which extends outwardly from body member 12. After clamping and sealing means 108 is telescoped over weather sleeve 104, with its second inner diameter 124 nearer to electrical contact 106 than its first inner diameter 122, a resilient gasket member 126 having an inside diameter substantially the same as the outside diameter of weather sleeve 104, is telescoped over the weather sleeve and disposed adjacent the shoulder 128 formed between the first and second inner diameters 122 and 124, respectively, of clamping and sealing means 108. Bushing connector 100, with electrical contact 106 in position, weather sleeve 104 disposed over insulation 112 of cable 102, and clamping and sealing means 108 and gasket member 126 in position on weather sleeve 104, may then be plugged into Opening 40 in body memher 12 until contact 106 is firmly in engagement with electrical contact 48. Clamping and sealing means 108 may then be advanced towards tubular metallic member 62, and turned to engage the threads of member 62 with the internal threads of clamping and sealing means 108. Clamping and sealing means 108 is turned until gasket member 126 is flattened between shoulder 128 and the outwardly extending end 71 of tubular member 62, which causes gasket member 126 to press tightly against weather sleeve 104 and provide a moisture seal, thus insuring that the electrical connection between contacts 106 and 48 will be sealed against moisture, even in the event the apparatus it is associated with is submerged in Water. After clamping and sealing means 108 is tightened against gasket member 126, clamping ring member 123 may be tightened to mechanically secure bushing connector 100 in assembled relation with body member 12. Thus, clamping and sealing means 108 cooperates with tubular member 62, gasket member 126, and weather sleeve 104, to provide a moisture seal, and it also cooperates with the weather sleeve 104 and tubular member 62 to mechanically secure the cable connector 100, and prevent the electrical cable 102 from being accidentally pulled out of the opening 40 in body member 12. While the length of weather sleeve 104 is not critical, it should be long enough to extend from a point near the end of the cable insulation 112, at the contact end of the cable 102, to a point beyond clamping and sealing means 108 when it is in its secured position relative to tubular member 62.

To make a quick but eifective sealed electrical connection to bushing assembly 10 at the point of use of its associated electrical apparatus, such as a distribution transformer, it is only necessary to remove a predetermined length of electrical insulation 112 from the end of cable 102, select an electrical contact 106 which has an inner diameter which closely matches the outside diameter of electrical conductor 110, telescope electrical contact 106 over the exposed end of electrical conductor 110, crimp, or otherwise secure electrical contact 106 to conductor 110, select a weather sleeve 104 which has an inner diameter which closely fits the outside diameter of cable 102, telescope weather sleeve 104 over the insulation 112 of cable 102, telescope clamping and sealing means 108 over weather sleeve 104, and telescope gasket memher 126 over weather sleeve 104. This completes bushing cable connector 100, and it is ready to be connected to bushing assembly 10. Cable connector 100 may be inserted into opening 40 in body member 12, until contact 106 snaps into contact 48. Clamping and sealing means 108 may then be turned onto tubular member 62 until gasket member 126 is compressed against weather sleeve 104, and clamping and sealing means 108 may then have its clamping ring 123 tightened to urge the inner diameter 122 of clamping means 108 against weather sleeve 104, to firmly secure cable 102 in assembled relation with bushing assembly 10.

It will be noted that the electrical connection between contact members 106 and 48 is made well within body portion 12 of the bushing assembly 10, preventing accidental contact with live terminals. This feature allows the electrical contacts to be sealed against moisture, and also allows the electrical connection to be made or broken without deenergizing the electrical conductor of the bushing, as long as cable 102 is not connected to a load.

In summary, there has been disclosed a new and improved electrical bushing assembly and bushing cable connector which allows a plurality of electrical cables to be quickly and reliably connected to, or disconnected from, an electrical bushing, using the load or service cables as bushing connectors. There are no exposed live terminals On the bushing assembly, which is a particularly desirable feature on distribution transformers associated with underground distribution of electrical power. It reducesthe hazard caused by foreign objects being pushed into the underground vaults or enclosures used to mount the distribution transformers, and it protects the electrical joint against moisture. Finally, these featuers and results are obtained with a relatively low cost, easily manufactured construction which completely eliminates the necessity of taping to provide electrical insulation and moisture-proof joints.

Since numerous changes may be made in the abovedescribed apparatus and diiferent embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. An electrical bushing assembly comprising a body member having first and second ends,

said body member being for-med of a cast resinous insulating material which defines at least two orifices which extend inwardly from the second end and terminate a predetermined distance from the first end of said body member,

an electrical conductor assembly having a first portion having first and second ends, and a second portion, said second portion being electrically connected to the second end of first portion and having at least two arms which project outwardly from said first portion,

a plurality of electrical contact members, one of each of said electrical contact members being electrically connected to each of the arms of the second portion of said electrical conductor assembly,

said electrical conductor assembly being embedded in said body member, with the first portion of said elec trical conductor assembly being disposed from the first end of said body member to a predetermined distance from the second end, each of the arms of the second portion of said electrical conductor assembly extending to one of the orifices of said body member, said electrical contact members being accessible from the second end of said body member through the orifices, plurality of tubular metallic members each having first and second ends, one of each of said tubular metallic members being disposed coaxially with each of the orifices in said body member, with the first ends of said tubular metallic members being embedded in said body member and the second ends of the tubular metallic members extending outwardly from the second end of said body member, metallic mounting flange, said metallic mounting flange having a portion circumferentially embedded in said body member, and resilient means disposed between the embedded portion of said metallic mounting flange and said body portion.

References Cited UNITED STATES PATENTS MARVIN A. CHAMPION, Primary Examiner. JOSEPH H. MCGLYNN, Assistant Examiner.

U.S. Cl. X.R. 339-88, 94, 103, 218; 174 -152 

